1. Field of the Invention
This invention relates to improvements in pressure gauges having pressure sensitive Bourdon tubes each operatively connected by an arcuate rack and pinion linkage to its rotating pointer of the dial and more particularly is directed to a magnetic drive between the rack segment and the pinion in place of conventional gear teeth.
2. Description of the Prior Art
A representative structural arrangement of Bourdon tube pressure gauges is shown in the drawing of U.S. Pat. No. 3,975,967 in which the relatively small movement of the Bourdon tube pressure sensitive free end 29 is connected by a linkage 30 to the amplifying movement 32 for rotating shaft 34 and pointer 36. Amplifying movement 32 comprises an arcuate rack segment which, when pivoted by the movement of Bourdon tube free end 29 through an acute angle, rotates the pinion mounted to turn shaft 34 and pointer 36. Amplifying movement 32 thus rotates pointer 36 through at least one complete rotation when Bourdon tube free end 29 moves between its limits. A hair spring, operating between shaft 34 and a portion of the housing, maintains a consistent and accurate reading by pointer 36 on dial 40 by taking up any slack in the gear teeth engagement between the rack segment and pinion. This geared rack segment and pinion with or without the hair spring biasing, has proved to be the weakest component in the gauge and is responsible for most of the failures and need for repairs. The hair spring has a tendency to break when abrupt movement of the mechanism occurs due to sudden pressure changes and the broken spring catches in the gear teeth. Also, these abrupt movements cause the teeth to wear excessively.
A need, therefore, exists for an improved movement amplifying mechanism which will eliminate the above described problems and provide a more reliable guage.